1. Field of the Invention
The invention relates to interconnect substrates such as a multi-chip substrate (MCS) by which a plurality of integrated chips can be interconnected into a multi-chip module (MCM).
2. Description of the Related Art
It has been long known that, by mounting a plurality of integrated chips on an interconnect substrate such as an MCS, the shorter paths between the chips result in faster switching. An interconnect substrate that includes a multi-level metal-polymer composite is described in U.S. Pat. No. 4,810,332, (Pan), incorporated herein by reference, which states that in copper/polyimide interconnects, the copper which is in contact with the polyimide will discolor indicating its oxidation or corrosion. Therefore an overconnect is provided to protect the copper from oxidation and enhance polyimide adhesion to copper. The protective coating can be nickel, chromium or other materials capable of being electroplated.
U.S. Pat. No. 4,702,792 (Chow et al.) discloses an interconnect substrate which is made using a polymeric photoresist which is patterned to form openings. Conductive material is then applied to fill the openings, and excess is removed by polishing to expose at least the exterior major surface of the polymeric material. The surface then consists of conductive lines and patterns surrounded by polymeric material. Preferred polymeric photoresists have a T.sub.g of at least 150.degree. C. and includes baked novolaks and polyimides.
U.S. Pat. No. 4,681,795 (Tuckerman) discloses planarizing the surface of each layer of a multi-level substrate by melting the metal using a pulsed laser prior to the patterning. As polyimides may be damaged by exposure to the molten metal, it is suggested that the dielectric be pure SiO.sub.2.
U.S. Pat. No. 4,770,897 (Wu) discloses the enhancing of adhesion between the copper and the polyimide of an interconnect substrate. This is done by completely sealing the copper in a cured dielectric sublayer having been applied as two materials, both preferably photosensitive polyimides that are cured in a vacuum at temperatures of 300.degree. C. or more.
The present inventors have now discovered that an interconnect substrate such as an MCS comprising a metal-polymer composite incorporating microelectronic circuitry like that described in the Pan patent, supra, can be made without any protective overcoating such as nickel or chromium when alternate layers of thermoset and thermoplastic resins which are free from copper reactive groups.